Simplify CMake if-statement variable references

Variables in CMake if-statements (and only in if-statements) do not need
to be explicitly dereferenced; a thing I did not always know.

CMake/GenerateMappings.cmake

@@ -23,18 +23,18 @@ endif()
 
 file(STRINGS "${source_path}" lines)
 foreach(line ${lines})
-    if ("${line}" MATCHES "^[0-9a-fA-F].*$")
-        if ("${line}" MATCHES "platform:Windows")
+    if (line MATCHES "^[0-9a-fA-F].*$")
+        if (line MATCHES "platform:Windows")
             if (GLFW_WIN32_MAPPINGS)
                 set(GLFW_WIN32_MAPPINGS "${GLFW_WIN32_MAPPINGS}\n")
             endif()
             set(GLFW_WIN32_MAPPINGS "${GLFW_WIN32_MAPPINGS}\"${line}\",")
-        elseif ("${line}" MATCHES "platform:Mac OS X")
+        elseif (line MATCHES "platform:Mac OS X")
             if (GLFW_COCOA_MAPPINGS)
                 set(GLFW_COCOA_MAPPINGS "${GLFW_COCOA_MAPPINGS}\n")
             endif()
             set(GLFW_COCOA_MAPPINGS "${GLFW_COCOA_MAPPINGS}\"${line}\",")
-        elseif ("${line}" MATCHES "platform:Linux")
+        elseif (line MATCHES "platform:Linux")
             if (GLFW_LINUX_MAPPINGS)
                 set(GLFW_LINUX_MAPPINGS "${GLFW_LINUX_MAPPINGS}\n")
             endif()